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Drouet of Monaco is the training partner of Bernard Tomic, Australia's top male tennis player

Tomic's burgeoning career has already been blighted by several off-court incidents

A lawyer representing the father of Australia's top-rated tennis player Bernard Tomic says John Tomic was acting in self-defense when he headbutted his son's training partner Thomas Drouet on Saturday.

On Monday, John Tomic, who is also his 20-year-old son's coach, denied a charge of assault in a Madrid court which ruled that a judge will decide his guilt or innocence at a hearing on May 14.

The incident -- which resulted in a broken nose for the Monegasque Drouet -- took place on Saturday afternoon outside the hotel in the Spanish capital where players were staying for the Madrid Masters.

Bernard was in town to contest the tournament only to suffer a first round at the hands of Radek Stepanek of the Czech Republic.

"I don't feel guilty. I did not do anything wrong," Tomic Senior told reporters of the fight.

His lawyer Carmen Dieguez said the reason that Tomic Snr used his head, rather than his arms, to attack Drouet was because the tennis player, 29, was holding the coach's arms at the time.

In a statement, Tennis Australia said they were awaiting further details before discussing the incident.

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"Obviously media reports regarding a recent incident are very concerning," the country's governing tennis body said. "We are working closely with ATP officials who are investigating the incident and are unable to comment further until the full facts are known."

The incident continues the mixed career of Bernard Tomic, ranked 53rd in the world, and who was dropped from his Davis Cup side earlier in the year for what Australia captain Pat Rafter called a lack of professionalism.

The youngster, who broke into the limelight when reaching the quarterfinals of Wimbledon as an 18-year-old, is no stranger to controversy involving his father, with the duo having been involved in several incidents.

Croatian-born John, who moved with his family to Australia when Bernard was three, has been coaching his son since he was 13, even though a man who used to drive taxis for a living had no previous tennis experience.

In 2009, John was forced to publicly apologize after telling his son to walk off court in the middle of a match against fellow Australian Marinko Matosevic in Perth as he was unhappy with the officiating.

Despite the incident resulting in a one-month ban from the International Tennis Federation, John was up to old his tricks a year later -- railing at Australian Open tournament director Craig Tiley so vehemently about the scheduling of one of his son's matches that security was ultimately placed around the official.

Last year, Tomic Junior was booed off court at Wimbledon, picking up a code violation after smashing his racket, as he made a first round exit before then requesting that his father should be ejected from the stands at the Miami Masters later in the year.

"I know he's my father but he's annoying me," Bernard, who was ranked as high as world no. 27 last year, stated to the match referee.

Tomic Senior has often clashed with Tennis Australia, having previously threatened to switch his son's allegiance to Croatia unless his demands are met.

Matters seemed to be improving as Bernard won his maiden ATP title in January but this latest incident appears to be yet another setback in a stop-start career for a player with a fine record at junior level.